The weapons are for using against their own residents. US residents need to pay taxes in USD. If they don't, weapons will be used to force them to pay (most pa

The weapons are for using against their own residents. US residents need to pay taxes in USD. If they don't, weapons will be used to force them to pay (most pay voluntarily, but if they escalate far enough, the weapons will come out). That means US residents need to acquire USD and are willing to trade valuable assets to do so. That makes USD valuable to US residents. US residents own many valuable non-fiat assets, so non-US residents know that they will be able to find a US resident who will trade them something valuable in exchange. That makes USD valuable to non-US residents. The same thing is true of more or less every fiat currency that has a non-negligible value.